This invention relates to semiconductor laser devices, and more particularly to improvements in a transverse junction stripe (which is abbreviated hereinafter to "TJS") type semiconductor laser device.
In semiconductor laser device, it is desirable to decrease the threshold current at which the laser oscillation is caused and there are already several known structures of a semiconductor laser device having decreased threshold currents. Among them, TJS type semiconductor laser devices have the particularly excellent structure by which a single mode oscillation is generated.
One of the known types of TJS semiconductor laser devices has comprised a substrate of gallium arsenide (GaAs) having a high resistivity and four semiconductor layers disposed in a superposed relationship on the substrate. Those four semiconductor layers have included aluminum gallium arsenide (AlGaAs) layers alternating gallium arsenide (GaAs) layers with the outermost layer formed of gallium arsenide. The four semiconductor layers have included one half having a P.sup.+ conductivity and the other half having an N type conductivity with a P type semiconductor zone interposed therebetween. By removing that portion of the P type semiconductor zone located in the outermost semiconductor layer, a groove has been formed to space the outermost layer into a P.sup.+ type and an N type layer portion, and a positive and a negative electrode have been disposed in ohmic contact with the P.sup.+ and N type layer portions respectively.
With a voltage applied across the positive and negative electrodes to render the former positive with respect to the latter, the greater part of the resulting current is concentrated into a PN junction adjacent to an activated layer region formed of that portion of the P type semiconductor zone located in the gallium arsenide layer nearer to the substrate resulting in the generation of a laser oscillation in that region.
When the semiconductor laser device as above described is disposed upside down on a heat sink, the groove formed in the outermost layer creates a void between the device and the heat sink with the result that this void prevents heat generated in the activated laser region from dissipating in the heat sink. This has given rise to problems in that the threshold current is not only increased but also the characteristics of the device are prematurely deteriorated.
Accordingly, it is an object of the present invention to provide a new and improved semiconductor laser device having a structure by which a surface portion of the device located in closest vicinity to an activated laser region involved can directly contact an associated heat sink to improve its heat dissipation and to thereby decrease the threshold current and increase the device lifetime as well as effecting a laser oscillation at a low threshold current, even at relatively high ambient temperatures.